1. Field of the Invention
This invention relates to a liquid-filled vibration isolating device or a so-called bush-type liquid-filled vibration isolating device suitable as an elastic bushing, an engine mount, a carburetor mount or the like, which serves to not only effectively damp low frequency, large amplitude vibrations but also sufficiently absorb high frequency, small amplitude vibrations from a vibration source.
2. Related Art Statement
In this type of the liquid-filled vibrations isolating device, there has hitherto been used, for example, a vibration isolating device comprising high-rigidity inner and outer sleeves concentrically arranged to each other, a rubber elastomer connecting the sleeves to each other, two liquid chambers formed in the rubber elastomer at its center in the axial direction and at opposite positions in the radial direction and filled with an imcomprenssible liquid, and at least one restricted passage communicating both liquid chambers with each other.
In such a vibration isolating device, when the vibration transmitted to the device is particularly low frequency, large amplitude vibrations (for example, vibrations with a frequency of less than 50 Hz and an amplitude of about .+-.1 mm), it can effectively be damped by converting kinetic energy of liquid into heat energy through flow resistance subjected to the liquid when the liquid flows from one of the liquid chambers to the other through the restricted passage.
In the conventional vibration isolating device, however, when the sectional area and length of the restricted passage communicating the liquid chambers with each other are selected so as to sufficiently damp vibrations in the low frequency range, the restricted passage is rendered into a choked state by inertia force, friction force and the like of liquid inside the restricted passage based on vibrations of relatively lower frequency in the high frequency range to thereby cause a rapid increase of dynamic spring rate, and consequently the insulation and damping of vibrations of higher frequency can hardly be expected.
On the other hand, when the dimension of the restricted passage is determined so as to sufficiently damp vibrations of high frequency zone, the damping of low frequency vibrations can not be expected.